UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

COLLEGE  OE  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


MEALY  BUGS  OF  CITRUS  TREES 


BY 

CURTIS  P.  CLAUSEN 


BULLETIN  No.  258 

Berkeley,  Cal.,  September,  1915 


UNIVERSITY   OF  CALIFORNIA  PRESS 

BERKELEY 

1915 


Benjamin  Ide  Wheeler,  President  of  the  University. 
EXPERIMENT  STATION  STAFF 

HEADS  OF  DIVISIONS 

Thomas  Forsyth  Hunt,  Director. 

Eugene  W.  Hilgard,  Agricultural  Chemistry  (Emeritus). 

Edward  J.  Wickson,  Horticulture  (Emeritus). 

Herbert  J.  Webber,  Director  Citrus  Experiment  Station;  Plant  Breeding 

Hubert  E.  Van  Norman,  Vice-Directcr;  Dairy  Management. 

William  A.  Setchell,  Botany. 

Myer  E.  Jaffa,  Nutrition. 

Robert  H.  Loughridge,  Soil  Chemistry  and  Physics  (Emeritus). 

Charles  W.  Woodworth,  Entomology. 

Ralph  E.  Smith,  Plant  Pathology. 

J.  Eliot  Coit,  Citriculture. 

John  W.  Gilmore,  Agronomy. 

Charles  F.  Shaw,  Soil  Technology. 

John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 

Frederic  T.  Bioletti,  Viticulture  and  Enology. 

Warren  T.  Clarke,  Agricultural  Extension. 

John  S.  Burd,  Agricultural  Chemistry. 

Charles  B.  Lipman,  Soil  Cnemistry  and  Bacteriology. 

Clarence  M.  Haring,  Veterinary  Science  and  Bacteriology. 

Ernest  B.  Babcock,  Genetics. 

Gordon  H.  True,  Animal  Husbandry. 

James  T.  Barrett,  Plant  Pathology. 

Fritz  W.  Woll,  Animal  Nutrition. 

A.  V.  Stubenrauch,  Pomology. 

Walter  Mulford,  Forestry. 

W.  P.  Kelley,  Agricultural  Chemistry. 

H.  J.  Quayle,  Entomology. 

Elwood  Mead,  Professor  of  Rural  Institutions. 

D.  T.  Mason,  Professor  of  Forestry. 

H.  S.  Reed,    Professor  of  Plant  Physiology. 

William  G.  Hummel,  Agricultural  Education. 

Leon  M.  Davis,  Dairy  Industry. 

John  E.  Dougherty,  Poultry  Husbandry. 

Frank  Adams,  Irrigation  Practice. 

David  N.  Morgan,  Assistant  to  the  Director. 

Mrs.  D.  L.  Bunnell,  Librarian. 

CITRUS  EXPERIMENT  STATION 

Division  of  Entomology 

H.  J.  Quayle  C  P.  Clausen 


MEALY  BUGS  OF  CITRUS  TREES* 

By  CURTIS  P.  CLAUSEN 


INTRODUCTION 

Among:  the  pests  of  citrus  trees  in  Southern  California,  the  mealy 
bugs  are  of  considerable  importance.  This  is  particularly  true  in  the 
coastal  regions,  where  conditions  of  humidity  and  temperature  are 
most  favorable  to  the  maximum  development  of  these  pests.  To  this 
susceptibility  to  climatic  influences  may  be  attributed,  in  part,  the 
comparative  slowness  of  the  spread  of  these  pests  over  the  citrus  section 
and  their  restriction  to  the  coastal  tier  of  counties,  thirty-five  years 
after  the  time  of  their  first  introduction.  In  the  interior  sections  the 
increase  in  numbers  is  not  nearly  so  rapid  and  it  is  only  in  occasional 
instances  that  an  infestation  becomes  serious  enough  to  require  ex- 
tensive control  measures.  While  in  the  aggregate  the  damage  caused 
by  these  pests  is  much  less  than  that  done  by  the  so-called  true  scale 
insects,  yet  in  particular  cases  the  injury  inflicted  has  resulted  in  a 
considerable  loss  of  fruit  and  in  an  extensive  dropping  of  foliage. 

SPECIES  CONCERNED 
The  total  number  of  mealy  bug  species  occurring  in  Southern 
California  is  about  twenty,  and  the  list  of  host  plants  upon  which 
these  occur  is  large  and  varied.  The  species  discussed  in  this  paper 
comprise  only  those  found  generally,  wherever  they  occur,  upon  citrus 
trees.  They  are  the  common  mealy  bug  (Pseudococcus  citri  Risso), 
Baker's  mealy  bug  (Pseudococcus  bakeri  Essig),  the  citrophilus  mealy 
bug  (Pseudococcus  citrophilus  Clausen  MSS),  and  the  long-tailed  mealy 
bug  (Pseudococcus  longispinus  Targ.).  Occasional  specimens  of  other 
species,  such  as  P.  ryani  (Ckll.)  and  Ceroputo  arctostaphylii  (Colm.), 
have  been  found  upon  citrus  trees,  but  their  presence  there  may  be 
considered  as  accidental.  Laboratory  experiments  have  borne  out  the 
assumption  that  they  exist  only  for  a  comparatively  short  time  solely 
upon  either  the  foliage  or  the  fruit  of  the  citrus  tree.  Separate  dis- 
cussions of  the  life  history  and  habits  of  the  different  species  will  be 
given  in  the  order  of  their  importance  as  citrus  pests  at  the  present 
time. 


*  Paper  No.  5,  Citrus  Experiment  Station,  College  of  Agriculture,  University 
of  California,  Riverside,  California. 

[19] 


20  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION 


Fig.  1.— Mealy  bugs  of  citrus  trees.  A.  The  long-tailed  mealy  bug 
(Pseudococcus  longispinus) .  B.  The  citrophilus  mealy  bug  (Pseudococcus 
citrophilus) .  C.  Baker's  mealy  bug  (Pseudococcus  bakeri).  D.  The  com- 
mon mealy  bug  (Pseudococcus  citri).     Enlarged  7  diam. 


MEALY   BUGS    OF    CITRUS    TREES  21 

GENERAL  DESCRIPTION 

The  mealy  bugs  are  characterized  by  the  possession,  in  the  female, 
of  a  more  or  less  dense  waxy  or  cottony  covering,  ordinarily  white  in 
color,  extending"  over  the  entire  upper  surface  and  in  most  cases  the 
lower  surface  also.  The  lateral  margin  of  the  body  bears  upon  each 
segment  a  filament  of  this  same  material,  which  arises  from  or  is 
secreted  by  glands  grouped  about  spines  of  greater  or  less  length. 
This  covering,  with  the  attendant  lateral  filaments,  is  secreted  by  the 
individual  after  each  moult,  the  body  of  the  larva  being  entirely 
devoid  of  protection  immediately  following  the  casting  of  the  skin, 
or  exuvium.  The  general  appearance  of  the  larva  is  very  similar  to 
that  of  the  adult. 

The  male,  in  its  early  stages,  greatly  resembles  the  female,  but 
when  it  is  about  one-fifth  the  length  of  the  adult  female  it  forms  a 
fibrous,  cottony  cocoon  about  one-eighth  of  an  inch  long,  within  which 
a  transformation  takes  place  and  from  which  the  adult  male  emerges 
as  a  small  two-winged  insect  of  very  delicate  structure. 

With  the  exception  of  the  male  pupa,  all  stages  of  this  insect 
following  the  newly  hatched  young  are  mobile,  and  movement  from 
place  to  place  may  be  observed  very  frequently. 

While  P.  longispinus  produces  its  young  alive,  the  species  previ- 
ously named  deposit  their  eggs  in  fairly  compact  ovisacs,  which  do  not 
envelop  the  female.  These  eg^  masses,  when  grouped  together  in  great 
numbers,  produce  the  cottony  masses  which  are  so  conspicuous  upon 
the  fruit,  and  to  a  lesser  degree  upon  the  foliage,  wherever  a  serious 
infestation  of  this  insect  occurs. 

THE  COMMON  MEALY  BUG 

(Pseudococcus  citri  Risso) 

General  Account! — This  species  is  by  far  the  most  injurious  member 
of  this  group  of  insects  and  in  the  aggregate  the  amount  of  damage 
done  exceeds  that  done  by  all  other  members  of  the  genus.  Over 
small  areas  it  is  as  serious  a  pest  as  any  of  the  scale  insects  known  to 
infest  citrus  trees  and  is  more  difficult  to  control.  Considering  the 
entire  citrus  district  of  Southern  California,  however,  this  pest  prob- 
ably ranks  sixth  in  the  total  amount  of  damage  done,  being  preceded 
by  the  black,  the  red,  the  purple,  the  citricola,  and  the  yellow  scales 
in  the  order  given. 

For  many  years  this  insect  has  been  a  more  or  less  serious  pest  in 
Florida.     Though  data  relative  to  its  introduction  into  California  is 


22  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

very  meager,  information  from  the  most  reliable  sources  available 
places  the  date  thereof  at  about  1880  and  the  place  San  Diego  County. 
Introduction  into  Ventura  County1  took  place  through  nursery  stock 
during  the  season  of  1897,  though  it  was  not  until  1908-09  that  the 
infestation  assumed  alarming  proportions.  The  year  1909  marked  the 
height  of  one  of  the  periods  of  heavy  infestation  by  this  species,  but 
since  that  time  the  damage  done  has  not  been  so  great.  This  general 
decline  in  destructiveness  cannot  be  attributed  entirely  to  the  control 
measures  employed  for  the  reason  that  badly  infested  groves  not  treated 
in  any  way  are  now  as  free  from  the  pest  as  those  in  which  control 
measures  were  employed. 

Nature  of  Injury. — The  injury  done  by  the  citrus  mealy  bug  con- 
sists of  a  general  withdrawal  of  sap  from  the  twigs  and  fruit,  the 
smutting  and  subsequent  dropping  of  the  foliage,  and  a  discoloration 
and  retardation  of  growth  in  the  fruit.  At  the  time  of  blossoming 
a  general  dropping  of  the  flowers  and  newly  set  fruit  often  takes  place 
where  the  young  mealy  bugs  assemble  in  large  numbers  in  the  calyx 
cup,  killing  the  plant  tissue  at  the  base  of  the  embryo.  The  larvae 
may  also  appear  in  large  numbers  upon  the  foliage,  withdrawing  sap 
and  chlorophyl  from  the  cells  and  thus  preventing  the  proper  func- 
tioning of  the  leaves.  The  smutting  of  the  foliage  is  very  extensive, 
the  mealy  bugs  in  all  the  larval  stages  exuding  large  quantities  of 
"honeydew",  in  which  the  black  sooty  mould  fungus,  Meliola  camelliae 
(Catt.)  grows.  This  may  be  so  great  as  to  cause  more  or  less  defoli- 
ation of  the  trees.  Quayle2  reports  this  condition  as  very  general  in 
the  citrus  districts  of  Sicily  during  the  year  1913. 

One  of  the  marked  habits  of  this  species  is  the  tendency  of  the 
larvae  and  adults  to  assemble  in  large,  compact  groups  upon  the  fruit 
and  branches.  In  the  case  of  oranges  this  causes  a  delay  in  the  color 
ation  of  that  area  of  the  fruit,  though  in  some  instances  an  unnatural 
reddish  color  is  produced  in  the  affected  areas.  As  far  as  could  be 
determined,  this  unnatural  coloration  was  not  due  to  the  presence  of 
a  fungus,  but  probably  to  some  change  of  the  cells  caused  by  the 
feeding  of  the  mealy  bugs.  The  effect  is  also  particularly  severe  upon 
navel  oranges,  where  large  masses  of  eggs  are  found  in  the  navel  end, 
which  often  bring  about  a  rapid  decay  of  this  portion  of  the  fruit. 
The  effect  upon  lemons,  aside  from  the  distortion  of  the  fruit  in  the 
younger  stages,  is  an  unevenness  in  coloration  and  premature  ripening. 
The  large  and  conspicuous  egg  masses  upon  the  fruit  give  it  a  very 


i  Essig,  E.  O.,  P.  C.  Jour.  Ent.,  Vol.  II,  No.  4,  p.  289,  December,  1910. 
2  Quayle,  H.  J.,  Citrus  Fruit  Insects  in  Mediterranean  Countries,  U.  S.  D.  A., 
Bull.  134,  p.  21  (1914). 


MEALY    BUGS    OF    CITRUS    TREES 


23 


unsightly  appearance,  and  the  presence  of  these  adds  greatly  to  the 
difficulty  of  controlling  the  insect. 

In  the  case  of  young  trees,  and  also  in  that  of  older  trees  that  have 
been  rebudded,  much  damage  is  often  done  by  the  massing  of  the 
mealy  bugs  upon  the  young  and  tender  shoots.  Often  these  shoots 
are  completely  killed,  necessitating  the  expense  of  rebudding.  On 
young  trees  the  injury  is  rarely  severe  enough  to  require  the  replace- 
ment of  the  tree. 

In  California  the  distribution  is  general  over  the  entire  state, 
though  in  the  northern  part  the  infestation  is  limited  largely  to  green- 


Tulore 


Son  Bernardino 


Riverside 


Fig.  2. — Map  indicating  distribution  of  common  mealy  bug 
{Pseudococcus  ciiri)  in  Southern  California 


houses  and  to  certain  ornamental  trees.  In  the  citrus  sections  of 
Butte  and  Yuba  counties,  however,  some  trouble  has  been  experienced 
from  the  attacks  of  this  insect.  In  Southern  California  the  infesta- 
tion of  this  pest  on  citrus  trees  is  confined  to  Santa  Barbara,  Ventura, 
Los  Angeles,  Orange,  and  San  Diego  counties.  It  occurs  elsewhere 
upon  ornamental  plants  and  in  greenhouses.  In  Santa  Barbara 
County,  where  conditions  are  apparently  satisfactory  for  the  maximum 
development  of  the  pest,  no  instance  of  a  severe  infestation  upon  an 
extensive  scale  has  been  reported,  and  a  recent  inspection  of  the  dis- 
trict by  the  writer  resulted  in  the  finding  of  the  pest  very  generally 


24 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 


on  ornamental  plants  and  occasionally  on  citrus  trees,  but  no  cases 
were  noted  in  which  serious  damage  had  been  done  in  commercial 
groves.  In  Ventura  and  Los  Angeles  counties  a  wide  distribution 
exists  and  a  number  of  groves  are  at  present  suffering  from  the  attacks 
of  this  pest,  though  as  a  whole  the  damage  done  is  less  than  that  of 
1909-10. 

Host  Plants. — Because  of  its  general  distribution  over  the  world, 
the  recorded  host  plants  of  this  species  are  numerous  and  of  widely 
different  forms.     A  list,  though  manifestly  incomplete,  is  here  given : 


Asparagus  (Asparagus  officinalis) 
Bird    of    Paradise    flower    (Strelitzia 

gigantea,  regina) 
Bottle-brush  (Callistemon  lanceolatus) 
Bouvardia  sp. 
California   laurel    (Umbellularia   cali- 

fomica) 
Cestrum  sp. 

Citron   (Citrus  medica  var.  genuina) 
Coffee   (Coffea  Arabica) 
Coleus  (Coleus  Blumei) 
Columbium  sp. 

Cotton  (Gossypium  peruvianum) 
Cranesbill  (Geranium  sp.) 
Cucumber  (Cucumis  sativus) 
Deer-brush  (Ceanothus  integerrimus) 
Dracaena    (Cordyline   terminalis) 
Hinglish  ivy  (Hedera  helix) 
Ferns 

Fuchsia  (Fucshia  sp.) 
Grape   (Vitis  vinifera) 
Granadilla  (Passiflora  edulis) 
Jasmine    (Gardenia  jasminoides) 
Leadwort  (Plumbago  sp.) 
Lemon  (Citrus  medica  var.  limon) 


Magnolia    (Magnolia  grandiflora) 
Moonflower   (Ipomoea  Bona-nox) 
Nettle  (Urtica  urens) 
Nightshade    (Solanum  douglasii) 
Oleander  (Nerium  oleander) 
Orange  (Citrus  aurantium) 
Panax  monstrosa 
Peony  (Paeonia  sp.) 
Pepino  (Solanum  muricatum) 
Phyllanthus  carolinensis 
Poinsettia  (Euphorbia  pulcherrima) 
Pomelo   (Citrus  decumana) 
Potato    (Solanum  tuberosum) 
Potato  vine  (Solanum  jasminoides) 
Pumpkin    (Cucurbita   pepo) 
Purple  passion-flower   (Passiflora 

violacea) 
Eedwood   (Sequoia  sempervirens) 
Eex  begonia  (Begonia  sp.) 
Tacsonia  jasminoides 
Tobacco  (Nicotiana  tabacum) 
Umbrella-plant  (Cyperus  alternif olius) 
Variegated    wandering-jew    (Zebrina 

pendula) 


Among  those  given,  the  coleus,  various  species  of  citrus,  nightshade, 
and  potato  vine  may  be  mentioned  as  preferred  hosts. 


LIFE  HISTORY 

The  Eggs. — The  eggs  are  deposited  by  the  female  upon  the  fruit, 
on  the  twigs  and  foliage,  and  under  loose  pieces  of  bark,  etc.  They 
are  enclosed  in  a  fairly  compact  network  of  interwoven  fibers,  giving 
the  general  appearance  of  a  light,  cottony  mass.  The  formation  of 
these  egg  masses  in  large  numbers  upon  the  fruit  gives  rise  to  the 
large  clusters,  observed  so  generally  upon  badly  infested  trees. 


MEALY   BUGS    OF    CITRUS    TREES  25 

The  number  of  eggs  deposited  by  a  single  female  ranges  from  300 
to  587,  as  determined  from  21  individuals,  the  average  being  483  eggs. 
The  time  required  for  oviposition  varied  from  6  to  14  days  under 
normal  summer  temperatures.  During  the  cooler  portions  of  the  year 
this  period  will  be  greatly  lengthened.  Hatching  takes  place  from  6 
to  10  days  after  the  eggs  are  laid,  though  during  the  winter  months 
several  weeks  may  be  required. 

Proportion  Hatching  and  Degree  of  Larval  Mortality. — Complete 
hatching  records  of  4000  eggs  give  the  proportion  hatching  as  91  per 
cent.  During  the  early  larval  stages  the  number  dying  from  various 
causes,  including  parasitic  and  predaceous  enemies,  is  very  great.  In 
all  probability  the  number  ultimately  reaching  maturity  even  in  cases 
of  very  serious  infestation  will  not  exceed  10  per  cent  of  the  whole 
number. 

The  Female. — The  newly  hatched  larvae  are  light  yellow  in  color 
and  devoid  of  any  waxy  covering,  which,  however,  soon  appears.  The 
periods  of  time  covered  by  the  three  larval  stages  in  24  individuals 
were  15,  16,  and  16  days  respectively.  Egg  laying  begins  approxi- 
mately two  weeks  after  the  third  and  final  moult,  and  death  takes  place 
as  soon  as  oviposition  is  completed. 

The  Male. — During  the  early  stages  very  little  distinction  can  be 
found  between  the  males  and  females.  The  formation  of  the  cocoon 
is  begun  about  four  weeks  after  hatching  and  the  adult  male  emerges 
10  to  14  clays  later. 

SEASONAL  HISTOEY 

There  is  very  little  differentiation  in  time  of  appearance  between 
succeeding  generations  in  this  species,  though  the  development  in  the 
late  winter  and  early  spring  is  quite  uniform.  This  condition,  how- 
ever, disappears  very  soon,  the  variation  in  the  development  of  the 
individuals  being  so  great  as  to  cause  a  complete  merging  of  succeeding 
generations,  so  that  during  the  summer  and  fall  months  all  stages  may 
be  found  upon  the  tree  in  large  numbers.  The  mealy  bug  passes  the 
winter  upon  the  tree  in  all  stages,  though  the  larger  proportion  are 
in  the  egg  stage.  The  eggs  are  laid  by  females  developing  slowly  and 
irregularly  during  the  late  fall  and  winter  months  and  remain  for 
a  considerable  time  without  hatching.  In  San  Diego  County  great 
masses  of  adults  and  eggs  have  been  observed  clustered  upon  the  trunk 
of  the  tree  from  the  surface  of  the  ground  to  six  inches  below.  Suffi- 
cient numbers,  however,  were  present  upon  the  fruit  and  foliage  to 
give  a  thorough  and  rapid  start  in  the  spring.     When  warm  weather 


26  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

appears  the  eggs  hatch  in  great  numbers  and  the  larvae  assemble  upon 
all  fresh  growth,  particularly  upon  young  fruit,  buds,  and  sucker 
growths.  It  is  at  this  time  that  much  injury  is  done  by  the  attacks 
upon  the  blossoms,  causing  a  marked  dropping  of  these,  and  of  the 
newly  set  fruit  as  well.  In  the  case  of  fruits  partially  developed  be- 
fore the  infestation  becomes  severe,  a  considerable  distortion  may  be 
brought  about  because  of  the  bugs  massing  upon  them  and  preventing 
their  proper  development.  The  spring  attack  is  usually  at  its  worst 
from  April  to  June.  Thereafter  the  high  summer  temperature  is 
apparently  not  conducive  to  the  maximum  development.  The  fall 
infestation  appears  during  early  September,  and  this  infestation  as 
it  develops  during  the  succeeding  months  is  the  more  severe  of  the  two. 


BAKER'S  MEALY  BUG 

(Pseudococcus  bakeri  Essig) 

General  Account. — This  mealy  bug  was  first  described  from  Santa 
Paula,  California,3  where  it  was  reported  as  occurring  generally  upon 
the  wralnut,  apple,  and  pear  trees  grown  in  the  citrus  section  of  Ven- 
tura County.  It  was  first  collected,  however,  upon  the  elder  (Sam- 
bucus  glauca) ,  which  grows  abundantly  in  the  waste  areas  in  the 
vicinity  of  Santa  Paula.  The  great  number  and  variety  of  its  host 
plants  and  its  distribution  generally  over  the  state  give  considerable 
support  to  the  belief  that  it  is  a  native  species.  Up  to  the  time  above 
noted,  however,  no  record  had  been  made  regarding  its  occurrence 
upon  citrus  trees,  and  the  fact  that  it  has  become  a  general  citrus  tree 
feeder  indicates  possibilities  along  this  line  in  the  case  of  other  species. 

Distribution. — The  range  of  distribution  of  this  species  is  con- 
stantly widening,  and  a  thorough  determination  of  its  limitations  will 
undoubtedly  reveal  it  in  many  sections  now  supposedly  uninfested. 
The  writer  has  found  it  upon  citrus  trees  in  Santa  Barbara,  Ventura, 
Los  Angeles,  Orange,  and  San  Diego  counties,  and  upon  native  and 
ornamental  plants  in  Riverside  and  in  San  Bernardino  counties.  It 
was  also  observed  upon  a  variety  of  plants  in  the  Botanical  Gardens 
at  Berkeley  and  has  been  reported  from  that  place  upon  the  walnut 
and  upon  the  California  buckeye.4  The  distribution,  therefore,  as 
far  as  is  now  known,  occurs  over  the  northern  and  central  parts  of 


3  Essig,  E.  O.,  P.  C.  Jour.  Ent.,  Vol.  II,  No.  4,  pp.  239-246,  December,  1910. 

4  Child's,  Leroy,  Monthly  Bulletin  Cal.   Hort.   Com.,   Vol.   Ill,   No.   5,   p.    220, 
May,  1914. 


MEALY   BUGS   OF    CITRUS    TREES 


27 


the  state  and  generally  over  Southern  California,  with  the  exception 
of  the  Imperial  Valley. 

Nature  of  Injury. — The  injury  occasioned  to  citrus  trees  is  not 
important  and  differs  in  no  marked  degree  from  that  produced  by  a 
light  infestation  of  the  common  mealy  bug.  The  full-grown  larvae 
and  adults  in  many  cases  under  observation  showed  a  strong  tendency 
to  confine  their  feeding  to  the  young  and  more  succulent  branches, 
and  they  clustered  in  considerable  numbers  in  the  crotches  of  the  small 
branches.     Where  fruit  is  present,  however,  many  mealy  bugs  in  all 


San  Bernardino 


Fig.  3. — Map  indicating  the  distribution  of  Baker's  mealy  bug 
(Pseudococcus  bakeri)  in  Southern  California 


stages  may  be  found  in  the  navels,  under  the  calyx  lobes,  and  at  the 
point  of  contact  of  fruits.  (See  fig.  5.)  Thus  far  no  infestation  has 
been  found  where  the  injury  to  the  fruit  or  tree  was  serious  enough 
to  require  control  measures. 

Host  Plants. — The  number  and  variety  of  host  plants  fostering  this 
species  is  large,  rather  incomplete  determinations  comprising  the  fol- 
lowing list.  The  elder,  walnut,  and  umbrella  plants  may  be  termed 
preferred  hosts,  though  this  is  quitely  largely  dependent  upon  the 
conditions  under  which  they  are  grown. 


28 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Apple  (Pyrus  mains) 
Buckeye  (Aesculus  calif  ornica) 
California   laurel    (Umbellularia   cali- 

f ornica) 
Candlenut    (Aleurites    triloba) 
Century  plant  (Agave  Americana) 
Coleus  (Coleus  Blumei) 
Cestrum    (Cestrum  elegens) 
Dracaena   (Cordyline  terminalis) 
Elder  (Sambucus  glauca) 
English  ivy   (Hedera  helix) 
Entcrolobium  sp. 
Horseweed  (Erigeron  canadensis) 
Iris  (7m  douglasiana) 
Japanese  quince  (Cydonia  japonica) 


Lemon  (Citrus  medica  var.  Union) 
Lemon  lily  (Lilium  Parryi) 
Lima  bean  (Phaseolus  lunatus) 
Mexican  orange  (Choisya  ternata) 
Nettle  (Urtica  urens) 
Nightshade  (Solatium  douglasii) 
Orange  (Citrus  aurantium) 
Pear  (Pyrus  communis) 
Potato  (Solanum  tuberosum) 
Potato  vine  (Solarium  jasminoides) 
SilK  oak  (Grevillea  robusta) 
Walnut  (Juglans  regia) 
Wild  sunflower  (Helianthus  annuus) 
Willow  (Salix  sp.) 
Windmill  palm 


j«ig>   4, — Baker's  mealy  bug    (Pseudococcus   baJceri)    congregated  at 
the  point  of  contact  of  two  fruits 


MEALY   BUGS   OF    CITRUS    TREES 


29 


LIFE  HISTORY 

The  Egg. — The  eggs  of  this  species  are  very  similar  in  general 
appearance  to  those  of  the  common  mealy  bug  and  are  laid  in  egg- 
sacs  measuring  one-fifth  to  one-third  of  an  inch  in  length.  The  number 
deposited  by  a  single  female  ranged  from  432  to  621  in  the  32  indi- 
viduals under  observation,  the  average  being  547  eggs.     The  time  in 


Fis 


5. — A  cluster  of  dates  infested  by  Baker's 
mealy  bug 


days  over  which  egg  laying  extended  ranged  from  7  to  15,  with  an 
average  of  10.3  days.  The  daily  average  would,  therefore,  be  approx- 
imately 53  eggs.  The  period  of  incubation  is  about  eight  days  during 
the  summer  and  considerably  longer  during  the  cooler  portions  of  the 
year. 


30  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION 

The  Female. — The  larvae  at  the  time  of  hatching  are  devoid  of  all 
waxy  covering,  but  its  secretion  is  soon  commenced.  At  the  end  of 
the  second  stage  the  wax  filaments  approximate  in  length  those  of  the 
adult  and  the  body  color  now  becomes  the  typical  slate  gray  of  the 
older  forms.  The  time  required  for  the  different  stages  is  quite  vari- 
able, but  the  records  of  21  individuals  gave  16.3,  13,  and  13  days 
respectively.  Egg-laying  commences  several  weeks  after  the  final 
moult,  the  females  in  the  meantime  having  grown  considerably,  the 
maximum  length  being  about  one-fourth  of  an  inch. 

The  Male. — The  formation  of  the  cocoon  begins  from  one  to  two 
weeks  after  hatching,  the  early  larval  stages  previous  to  this  time 
being  very  similar  to  those  of  the  female.  The  period  of  time  passed 
within  the  cocoon  is  about  nine  days,  at  the  end  of  which  time  the  adult 
male  emerges. 


THE  CITROPHILUS  MEALY  BUG 

(Pseudococcus  citrophilus  Clausen  MSS) 

General  Account. — During  the  fall  of  1913  there  was  discovered 
in  a  restricted  locality  near  Uplands,  California,  an  infestation  of 
mealy  bugs  in  a  number  of  groves.  On  the  basis  of  no  definite  deter- 
minations of  the  specific  identity  of  the  insect,  it  was  assumed  by  the 
growers  to  be  the  common  mealy  bug  (P.  citri) ,  and  much  alarm  was 
felt  by  the  growers  over  the  unexpected  invasion  of  this  pest  into  the 
interior  valley,  where  it  supposedly  would  not  thrive  because  of  ad- 
verse climatic  conditions.  Much  damage  was  done  to  certain  groves 
in  a  hasty  attempt  to  eradicate  the  pest,  the  loss  being  estimated  at 
approximately  $15,000.  In  order  to  secure  more  accurate  and  reliable 
ib formation  as  regards  ways  and  means  of  control,  an  Emergency 
State  Fruit  Growers'  Convention  was  called  at  Ontario,  California, 
January  30,  1914,  at  which  time  extended  discussions  were  given  by 
growers  and  investigators  upon  the  various  phases  of  the  problem, 
referring  mainly,  however,  to  the  common  mealy  bug  (P.  citri). 
Specific  determinations  made  at  this  time  indicated  that  the  insect 
was  Baker's  mealy  bug  (P.  oakeri) ,  a  native  species  known  at  that 
time  to  occur  only  in  Ventura  County,  where  it  was  present  on  many 
wild  plants  and  to  a  limited  extent  upon  citrus  trees.  The  particular 
differences  in  characters  which  led  to  the  determination  of  the  Uplands 
form  as  a  new  species  will  be  discussed  in  a  later  publication. 

Nature  of  Injury. — The  actual  damage  thus  far  produced  has  not 
been  great,  though  the  loss  entailed  by  attempted  eradication  was  con- 


MEALY   BUGS   OF    CITRUS    TREES 


31 


siderable.  In  the  worst  infested  groves,  a  slight  dropping  of  the 
flowers  and  young  fruit  upon  lemon  trees  was  noticeable,  and  also  a 
smutting  of  the  tree  during  the  early  spring  and  summer  months. 
Some  discoloration  of  oranges  was  observed  and  an  occasional  infection 
of  the  navel  end  brought  about  by  the  mealy  bugs  clustering  therein, 
but  this  condition  was  not  extensive.  The  habit  of  gathering  in  large 
clusters,  so  characteristic  of  the  common  mealy  bug,  is  almost  entirely 
absent  in  this  species,  thus  eliminating  to  some  extent  the  large  egg 
masses  upon  the  fruit,  such  as  are  so  noticeable  in  the  case  of  an 
infestation  of  the  former  species. 


Kines 


San  Bernardino 


Fig.  6. — Map  showing  distribution  of  citrophilus  mealy  bug 
(Pseudococcus  citrophilus)  in  Southern  California 

General  Description. — A  comparison  of  this  form  with  typical 
specimens  of  Baker's  mealy  bug  from  Ventura  showed  a  considerable 
difference  in  general  appearances,  and  led  to  the  belief  that  possibly 
the  infestation  at  Uplands  was  by  an  entirely  different  species,  rather 
than  by  the  one  occurring  upon  citrus  trees  in  Ventura  County.  These 
differences,  in  connection  with  several  structural  characters,  ultimately 
led  to  the  determination  of  this  form  as  a  new  species. 

In  the  case  of  Baker's  mealy  bug,  the  fine  waxy  secretion  is  evenly 
deposited  over  the  entire  surface  of  the  body,  while  the  lateral  fila- 
ments are  of  a  delicate,  thread-like  appearance  and  averaging  not 
more  than  one-fourth  the  width  of  the  body.     The  caudal  filaments 


32  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

are  of  the  same  general  form  but  longer,  being  from  one-third  to  one- 
half  the  length  of  the  body.  As  contrasted  with  this,  the  citrophilus 
mealy  bug  presents  a  decidedly  different  appearance,  the  waxy  cover- 
ing of  the  body  being  of  a  much  more  granular  texture  and  deposited 
unevenly  over  the  surface. 

A  detailed  description  of  this  species  is  now  in  course  of  prepar- 
ation and  will  shortly  be  available  for  those  desiring  to  make  a  more 
technical  study  of  its  taxonomic  characters. 

Distribution. — This  species,  on  the  basis  of  our  present  knowledge 
of  its  habits  and  distribution,  is  strictly  limited  to  a  district  of  ap- 
proximately one  square  mile  in  area,  near  Uplands,  California.  The 
infestation  has  spread  considerably  since  its  discovery  in  1913,  the 
number  of  groves  in  which  the  pest  can  now  be  found  being  nearly 
twice  the  number  determined  at  that  time. 

Origin  of  the  Infestation. — All  clues  bearing  upon  the  introduction 
of  this  pest  have  failed  to  give  any  positive  information  as  to  either 
the  time  or  source  of  the  original  importation.  During  the  year  1910 
a  considerable  number  of  imported  ornamental  plants  were  brought 
in  and  planted  near  the  center  of  the  present  infested  area.  These 
plants,  according  to  the  horticultural  inspector  of  that  district,  were 
not  examined,  and  the  presence  or  absence  of  pests  upon  them  at  that 
time  cannot,  therefore,  be  determined.  The  infestation  seems  to  have 
spread  quite  uniformly  from  this  central  point,  and  the  assumption 
of  these  growers  that  the  insect  was  .brought  in  upon  certain  of  these 
plants  is,  in  the  absence  of  positive  evidence  to  the  contrary,  fairly 
logical.  That  it  is  an  introduced  species  seems  to  be  established  with 
a  considerable  degree  of  certainty,  and  a  study  of  its  rate  of  increase 
and  methods  of  dispersion  have  lead  to  the  conclusion  that  the  year 
1910  marks  approximately  the  time  of  introduction. 

Host  Plants. — In  so  far  as  they  have  been  determined,  the  host 
plants  of  this  species  are  confined  to  the  following  series : 

Azalea   {Azalea  sp)  Pepper  tree  (Shinus  molle) 

Blackberry   (Rubus  villosus)  Pigweed  (Chenopodium  album) 

Climbing  fig  (Ficus  pumila)  Potato  (Solatium  tuberosum) 

English  Ivy  (Hedera  helix)  Easpberry   (Rubus  nutTcanus) 

Fig  (Ficus  carica)  Rhubarb    (Rheum  rhaponticum) 

Heliotrope  (Heliotropium  sp.)  Rose  (Rosa  sp.) 

Lemon  (Citrus  medica  var.  limon)  Rye  grass   (Lolium  perenne) 

Mallow  (Malva  parviflora)  Silk  oak  or  Grevillea   (Grevillea 
Mexican  orange  (Choisya  ternata)  robusta) 

Mustard  (Brassica  nigra)  Sweet  Clover  (Melilotus  alba) 

Nightshade  (Sola?ium  douglasii)  Sunflower  (Helianthus  annuus) 

Orange   (Citrus  aurantium)  Walnut   (Juglans  regia) 


MEALY   BUGS   OP    CITRUS   TREES  33 

It  must  be  remembered  in  connection  with  the  list  of  host  plants, 
however,  that  these  in  every  case  were  closely  adjacent  to  infested 
citrus  trees,  and  individuals  upon  these  plants  do  not  necessarily 
indicate  that  the  complete  life  cycle  could  be  accomplished  solely  upon 
this  particular  host.  The  infestation  was  particularly  severe  upon  the 
grevillea,  rhubarb,  and  potato,  even  more  so,  in  fact,  than  upon  nearby 
citrus  trees.  Potato  vines  were  in  many  cases  completely  killed,  the 
mealy  bugs  becoming  thickly  massed  upon  the  stems  and  upper  roots, 
and  in  some  cases  extending  even  down  upon  the  tubers  themselves. 
Upon  the  grevillea,  in  the  early  spring  particularly,  the  young  bugs 
were  commonly  found  densely  clustered  about  the  base  of  newly  de- 
veloping shoots.  Later  in  the  season  their  activities  were  confined 
largely  to  the  tender  growth  upon  the  margins  of  injured  areas  and 
upon  other  more  succulent  areas.  Rhubarb  grown  in  the  immediate 
vicinity  of  infested  trees  was  very  severely  attacked,  the  insects  being 
densely  massed  upon  the  leaves,  petioles,  and  also,  to  a  considerable 
extent,  upon  the  tubers  below  the  surface  of  the  ground. 

LIFE  HISTOEY 

The  Egg. — The  number  of  eggs  deposited  by  a  single  female  is 
somewhat  greater  than  in  the  other  species  discussed,  the  range  being 
from  394  to  679  for  the  entire  period,  averaging  533  eggs  for  40  indi- 
viduals. Upon  a  daily  basis,  this  represents  62  eggs,  though  in  one 
instance  127  eggs  were  deposited  by  a  single  female.  The  period  of 
oviposition  ranges  from  seven  to  ten  days  under  normal  conditions. 

The  Female. — The  larvae  at  the  time  of  hatching  are  about  one- 
fortieth  of  an  inch  in  length  and  yellow  in  color,  though  this  changes 
to  a  deep  amber  in  the  later  stages.  The  three  moults  take  place  at 
intervals  of  15,  13,  and  12  days  respectively.  In  all  respects  except 
that  of  size,  the  larvae  after  the  second  moult  are  similar  to  the  adults. 
Previous  to  this  time  the  ridged  appearance  is  noticeable  to  a  certain 
extent,  and  also  the  long  caudal  filaments.  During  the  adult  stage 
occasional  individuals  are  almost  entirely  devoid  of  the  waxy  covering 
on  the  upper  surface. 

The  Male. — The  formation  of  the  cocoon  is  begun  by  the  larvae 
about  twenty-five  days  after  hatching,  and  the  adult  male  emerges 
nine  to  eleven  days  later. 

SEASONAL  HISTORY 
The  first  generation  of  any  size  during  the  spring  of  1914  hatched 
during  March  and  reached  maturity  the  latter  part  of  April.     Ovi- 
position took  place  generally  during  the  month  of  April,   and  the 


34 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 


second  generation,  of  considerable  size,  began  to  appear  about  the  first 
of  May.  The  numbers  were  very  great  at  this  time,  and  shortly  after- 
wards a  slight  dropping  of  the  young  fruit  was  noticed,  due  to  the 
clusters  of  young  mealy  bugs  in  the  calyx  cup.  A  considerable  black- 
ening of  the  interior  foliage  of  the  lemon  trees  was  apparent.  The 
marked  migratory  habit  of  the  females  was  also  observed  at  this  time. 
This  generation  reached  maturity  during  the  early  part  of  June.  In 
numbers  of  adults  present,  this  was  the  largest  generation  of  the  year, 
the  summer  heat  following  shortly  afterwards  apparently  having  the 
effect  of  killing  off  manv  of  the  individuals  in  the  vounger  stages. 


\  >.■/,-    ;;'"':"-      ' 


Fig.  7. — Grevillea  trees  topped  in  an  effort  to  prevent  the  spread  of  the 
citrophilus  mealy  bug  (P.  citrophilus) 

The  third  generation  appeared  in  adult  form  during  the  latter  part 
of  July  and  the  first  week  in  August.  From  July  10  to  20  very  few 
mature  females  and  egg  masses  could  be  found,  and  this  was  in  many 
ways  the  most  distinct  generation  of  the  year.  In  contrast  with  those 
of  the  second  generation,  the  females  were  considerably  reduced  in 
size,  due  perhaps  to  the  extreme  heat. 

The  limits  of  the  fourth  generation,  while  noticeable,  were  not  as 
distinct  as  those  of  the  two  previous  generations.  A  considerable 
decrease  in  numbers  was  observed.  The  adults  appeared  in  greatest 
numbers  about  the  first  of  October,  and  oviposition  took  place  irreg- 
ularlv  after  this  time. 


MEALY   BUGS   OF    CITRUS   TREES  35 

No  distinction  in  generations  could  be  determined  from  this  time 
on,  and  upon  the  citrus,  development  was  greatly  inhibited,  to  a  con- 
siderable extent  at  least.  All  stages,  however,  could  be  found  upon 
the  fruit  throughout  the  winter,  though  the  adult  females  were  very 
scarce.  First  and  second  stage  larvae  were  found  in  considerable 
numbers  in  the  depressions  on  the  surface  of  the  fruit.  In  contrast 
to  this,  on  the  grevillea  trees  bordering  the  infested  groves  a  large 
proportion  of  those  found  were  in  the  adult  stage,  though  oviposition 
was  not  general.  Upon  rhubarb  the  infestation  throughout  the  winter 
was  very  heavy,  upon  the  leaves  as  well  as  upon  the  roots.  None  were 
found  upon  the  roots  of  citrus  trees. 

The  most  noticeable  feature  of  the  seasonal  history  of  this  species, 
and  in  marked  contrast  to  that  of  those  previously  discussed,  is  the 
remarkable  distinctness  of  the  generations  throughout  the  major  por- 
tion of  the  year,  and  this  feature  is  of  considerable  value  in  the  deter- 
mination of  methods  of  control  and  the  time  of  application.  Whether 
this  will  hold  when  an  infestation  becomes  very  severe  remains  to  be 
seen,  but  under  present  conditions  this  characteristic  holds  true  to  a 
marked  degree. 


THE  LONG-TAILED  MEALY  BUG 

(Pseudococcus  longispinus  Targ.) 

General  Account. — Among  the  most  common  of  the  greenhouse 
pests  will  be  found  usually  the  long-tailed  mealy  bug,  so  termed  be- 
cause of  its  unusually  long  caudal  filaments,  these  often  being  much 
longer  than  the  body.  While  not  occurring  to  any  extent  upon  citrus 
trees,  it  is  often  found  upon  those  growing  in  sheltered  and  protected 
places,  and  for  this  reason  would  be  classed  among  the  citrus  pests 
of  this  group. 

Distribution. — This  species  is  a  common  pest  in  nearly  all  of  the 
tropical  and  subtropical  regions  of  the  world,  and  also  in  greenhouses 
in  the  colder  countries.  In  Southern  California  it  has  been  found  in 
Santa  Barbara,  Ventura,  Los  Angeles,  Orange,  anu  San  Diego  counties. 
It  has  also  been  found  on  nursery  stock  in  Riverside  and  San  Ber- 
nardino counties,  which  had  previously  been  brought  in  from  other 
sections.  To  the  writer's  knowledge,  however,  no  general  nursery 
infestations  are  present  in  these  two  counties.  Its  presence  upon  the 
citrus  trees  is  confined  largely  to  the  coast  counties,  particularly  Santa 
Barbara  and  Ventura. 


36 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


DISTRIBUTION  CHART 
Host  Plants. — The  list  of  host  plants  of  this  species  indicates  that 
it  is  a  general  feeder  upon  most  greenhouse  plants,  and  also  upon  a 
considerable  number  growing  in  the  open.  The  following  series  com- 
prises the  complete  list  as  previously  published,  and  also  those  deter- 
mined by  the  writer. 
Begonia  (Begonia  sp.) 
Bird    of    Paradise    flower    (Strelitzia 

gigantea) 
Calla   (Ehicardia  Africana) 
Candlenut  (Aleurites  triloba) 
Century  plant    (Agave  Americana) 
Cineraria   (Cineraria  cruenta) 
Citron  (Citrus  medica  var.  genuina) 
Coleus  (Coleus  Blumei) 
Crab  cactus  (Epiphyllum  sp.) 
Croton  (Croton  Tiglium) 
Damolya  spectabilis 
Dracaena    (Cordyline   terminalis) 
Ferns 

Fig  (Ficus  carica) 
Flacourtia  sepiaria 
Fuchsia  (Fuchsia  sp.) 
Guadalupe  Island  palm  (Erythea 

edulis) 


Guava  (Pisdium  guajava) 
Lemon  (Citrus  medica  var.  limon) 
Mango   (Mangifera  Indica) 
Moonflower   (Ipomoea  Bona-nox) 
Nephrodium  amplum 
Oleander  (Nerium  oleander) 
Prickly  pear  (Opuntia  sp.) 
New  Zealand  Flax   (Phormium  tenax 

var.  variegatum) 
Plum  (Prunus  domestica) 
Primrose  (Primula  obconica) 
Sago  palm  (Cycas  revoluta) 
Staghorn  ferm  (Platycerium  sp.) 
Stangeria  schizodon 
Sterculia  gregori 

Umbrella-plant  (Cyperus  alternifolius) 
Zamia  sp. 


San  Bernardino 


Fig.  8. — Map  indicating  distribution  of  the  long-tailed  mealy 
bug  (P.  longispinus  Targ.) 


MEALY   BUGS   OF    CITRUS    TREES  37 

In  the  coast  counties  particularly  the  Dracaenas  under  normal  out- 
door conditions  are  very  heavily  infested,  thereby  rendering  them 
unsightly  and  of  little  value  for  ornamental  purposes.  In  some  cases 
a  complete  killing  of  the  plant  is  brought  about.  The  mealy  bugs 
cluster  thickly  on  the  under  sides  of  the  leaves  and  at  the  base  of  the 
growing  portion  of  the  top.  In  the  greenhouses  the  growing  tips  of 
the  plants  often  become  so  thickly  covered  with  the  young  mealy  bugs 
as  to  seriously  retard  growth,  or  to  cause  the  death  of  the  plant. 

A  number  of  the  host  plants  as  above  enumerated  were  found  only 
in  ornamental  gardens  and  are  of  rare  occurrence  in  this  region,  being 
largely  tropical  plants  imported  in  very  limited  numbers. 

LIFE  HISTORY 

Manner  and  Rate  of  Reproduction. — Unlike  the  species  previously 
considered,  this  mealy  bug  deposits  no  eggs,  but  reproduces  itself  by 
means  of  the  production  of  living  young.  The  female,  therefore,  forms 
no  egg-sac,  but  merely  secretes  about  her  body  a  thinly  woven  cottony 
network,  within  which  the  young  are  born  and  sheltered  for  a  time 
before  feeding  begins.  Considerable  difficulty  was  experienced  in 
securing  the  rate  of  larvaposition,  due  to  the  disturbing  effect  upon 
the  female  occasioned  by  the  daily  removal  and  counting  of  the  young. 
Records  of  15  individuals,  kept  through  the  entire  adult  period,  gave 
a  range  in  the  length  of  the  period  of  larvaposition  of  from  10  to  21 
days,  averaging  15.8  days.  The  largest  number  of  young  produced 
by  a  single  female  in  one  day  was  37,  and  for  the  entire  period  321 
young.  The  totals  for  all  specimens  averaged  206,  which,  when  re- 
duced to  a  daily  basis,  represents  13  young  per  day.  From  this  it 
will  be  seen  that  the  rate  of  increase  is  considerably  slower  than  in 
any  of  the  preceding  three  species,  the  progeny  of  one  individual 
numbering  less  than  half  that  of  the  common  mealy  bug  (P.  citri)  and 
somewhat  more  than  one-third  that  of  the  citrophilus  mealy  bug  (P. 
citrophilus) . 

Mortality  in  Various  Stages. — It  was  found  that  the  mortality 
during  the  first  larval  period  was  far  greater  in  this  species  than  in 
any  of  the  three  species  previously  discussed.  The  young,  remaining 
clustered  under  the  body  of  the  parent  for  one  or  more  days  after 
birth,  are  well  protected  from  sudden  changes  of  the  various  climatic 
conditions,  but  after  their  emergence  from  this  protection  the  death 
rate  is  greatly  increased.  After  this  first  larval  period,  the  mortality 
may  be  termed  normal  as  compared  with  that  of  the  other  species. 
There  being  none  of  the  large  egg  masses  present,  the  opportunity 


38  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

for  extensive  work  by  predaceous  enemies  is  somewhat  lessened,  though 
the  number  and  effectiveness  of  internal  parasites  is  slightly  greater. 
The  Female. — The  periods  of  time  required  for  the  different  stages 
were  decidedly  variable,  the  first  being  completed  in  from  10  to  20 
days  after  birth ;  the  second,  8  to  22  days  later ;  and  the  third,  7  to  20 
days  afterwards.  The  averages  of  these  periods  for  all  individuals 
under  observation  were  16.5,  15,  and  12.5  days  respectively.  Fertil- 
ization takes  place  largely  during  the  third  larval  period,  and  larva- 
position  begins  within  10  to  15  days  after  the  casting  of  the  third 
larval  skin. 

SEASONAL  HISTOKY 

No  particular  distinctions  between  generations  can  be  found  at 
any  time  of  the  year.  Reproduction  naturally  is  more  rapid  during 
the  warmer  months  than  during  the  winter,  and  the  infestation  is 
usually  at  its  height  during  the  fall  months.  From  January  to  March 
the  production  of  young  is  inhibited  by  adverse  climatic  conditions, 
but  this  period  is  so  short  as  to  cause  no  appreciable  diminution  in 
the  infestation. 


PARASITES  AND  PREDACEOUS  ENEMIES 
It  is  not  proposed  to  give  here  an  extended  and  detailed  discussion 
of  the  mealy  bug  parasites  of  California,  this  being  reserved  for  a 
later  paper.  The  various  enemies  here  considered  are  given  in  the 
order  of  their  relative  value  as  mealy  bug  destroyers,  though  aside 
from  the  first  five  their  occurrence  is  so  limited  as  to  make  an  accurate 
study  of  their  comparative  efficiency  impossible. 

The  Brown  Lacewing  (Sympherobius  calif  ornicns  Banks). — This 
lacewing  is  by  far  the  most  effective  of  the  entire  series  of  mealy  bug 
predators.  Its  distribution  is  quite  general  throughout  the  entire 
infested  area,  though  at  Uplands,  California,  it  is  found  only  very 
occasionally  in  connection  with  the  infestation  of  V .  citrophilus.  The 
eggs  are  pearly  white  in  color,  and  are  deposited  by  the  female  upon 
the  surface  of  the  fruits  and  leaves  or  within  the  egg  masses  of  the 
host.  Several  cases  were  observed  where  the  egg  was  laid  directly  upon 
the  body  of  the  live  mealy  bug.  The  larvae,  upon  emergence  from  the 
eggs,  immediately  move  about  in  search  of  food.  The  adults  are  also 
very  active  feeders  upon  the  younger  stages  of  the  mealy  bug,  though 
the  number  consumed  is  not  nearly  so  great  as  by  the  larvae  in  the 
later  stages.  The  adult  life  extends  normally  over  a  period  of  from 
one  to  three  weeks. 


MEALY   BUGS   OF    CITRUS   TREES  39 

Preying  upon  the  immature  stages  of  this  lacewing  and  greatly 
reducing  its  effectiveness  is  a  small  hymenopterous  parasite  (Isodro- 
mus  iceryae  How.),  which  deposits  its  egg  within  the  body  of  the  larva 
and  brings  about  its  death  after  pupation  has  taken  place. 

Leucopis  bella  Loew. — This  small  fly  is  found  in  comparatively 
large  numbers  in  practically  all  sections  infested  with  the  mealy  bug, 
and  is  the  only  enemy  of  P.  citrophilus  of  any  importance.  The  egg 
is  pearly  white  in  color,  oblong  in  form,  quite  strongly  pointed  at 
one  end,  and  bears  upon  the  surface  delicate  longitudinal  ridges. 
These  eggs  are  deposited  by  the  fly  singly  upon  or  under  the  egg 
masses,  and  the  young  at  the  time  of  hatching  commence  feeding 
upon  the  eggs  and  newly  hatched  larvae  of  the  host.  In  the  case  of 
the  more  mature  individuals,  instances  have  been  noted  in  which  the 
larva  attached  itself  to  the  body  of  an  adult  mealy  bug,  though  appar- 
ently unable  to  bring  about  its  death.  The  cocoons  are  formed  either 
within  the  egg  masses  or  in  various  protected  places,  a  favorite  position 
being  under  fragments  of  loose  bark  or  in  dried  or  curled  leaves. 

Cryptolaemiis  montrouzieri  Muls. — Much  has  been  claimed  for  this 
coccinellid  as  a  natural  enemy  of  the  mealy  bug  in  southern  California 
since  its  introduction  into  the  state  by  Alfred  Koebele  some  time  be- 
tween 1890  and  1895.  In  1909  it  was  introduced  into  Ventura  County 
and  during  the  following  season  was  reported  to  have  done  remarkable 
work.  At  present  only  occasional  specimens  can  be  found,  even  in 
heavily  infested  groves,  and  there  is  little  reason  to  believe  that  this 
parasite  is  in  any  very  large  measure  responsible  for  the  general 
decline  in  the  severity  of  the  mealy-bug  infestation  in  that  county 
since  that  time. 

In  San  Diego  County  several  isolated  instances  of  fairly  effective 
work  have  been  observed,  but  efforts  to  secure  a  general  distribution 
and  effectiveness  over  the  entire  infested  area  have  not  resulted  satis- 
factorily. Repeated  attempts  to  introduce  this  enemy  into  the  valleys 
not  immediately  adjacent  to  the  coast  have  uniformly  resulted  in 
failures.  From  these  results  it  appears  that  there  is  very  little  hope 
for  satisfactory  results  outside  of  certain  limited  areas  near  the  coast, 
where  the  temperature  and  humidity  conditions  are  more  favorable 
for  the  development  of  the  insect.  One  factor  which  prevents  more 
effective  work  on  the  part  of  this  predator  is  its  inability,  or  at  least 
lack  of  inclination,  to  spread  to  any  extent  from  tree  to  tree,  or  from 
grove  to  grove.  Infested  trees  have  been  found  in  which  the  beetles 
and  their  larvae  were  present  in  large  numbers,  and  immediately 
adjoining  these  were  other  trees,  also  well  infested,  upon  which  prac- 
tically none  could  be  found. 


40  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

The  Green  Lacewing  (Chrysopa  calif omica  Coq.). — This  delicate 
lacewing,  while  primarily  an  aphis  feeder,  is  often  found  in  consid- 
erable numbers  in  connection  with  mealy-bug  infestations.  Feeding 
is  quite  extensive  by  both  larvae  and  adults,  the  younger  stages  of 
mealy  bugs  ordinarily  being  attacked.  The  eggs  are  small,  ovoid,  and 
light  green  in  color  and  are  attached  to  the  end  of  a  large  stalk.  The 
larvae  hatch  and  immediately  crawl  about  in  search  of  food.  The 
long,  sickle-shaped  jaws  enable  them  to  pierce  the  body  of  the  mealy 
bug  easily  and  to  extract  the  body  juices.  At  the  time  of  pupation 
the  larva  forms  a  thin  but  very  dense  white  cocoon  about  itself  and 
undergoes  its  transformation.  About  this  main  pupal  case  is  found 
ordinarily  an  indefinite  fibrous  web,  which  serves  to  hold  it  in  place. 
The  cocoons  are  usually  placed  in  crevices  in  the  bark,  etc.,  but  as  a 
general  rule  are  more  exposed  and  conspicuous  than  those  of  the  brown 
lacewing  (S.  calif  ornicus  Banks). 

Scymnus  guttulatus  Lee. — This  minute,  native  coccinellid  is  re- 
stricted in  distribution  to  the  coast  counties,  and  its  work  is  confined 
largely  to  the  mealy  bugs,  though  feeding  has  been  occasionally  ob- 
served upon  the  young  of  the  black  scale.  While  no  instances  of 
satisfactory  control  under  field  conditions  have  come  to  our  attention, 
yet,  in  connection  with  other  parasites  and  predaceous  enemies,  the 
aggregate  effect  is  often  appreciable. 

Scymnus  bipunctatus  Kugel. — The  first  introduction  of  this  pred- 
ator was  brought  about  by  George  Compere  from  the  Philippine  Islands 
in  1910.  It  was  introduced  under  the  name  of  Crypt  ogonus  orbiculus. 
and  has  been  known  as  such  since  that  time.  Recent  determinations 
by  Smith,5  however,  give  the  identification  as  8.  bipunctatus.  Since 
1910  a  fairly  general  distribution  throughout  Ventura  and  Santa 
Barbara  counties  has  been  effected,  though  the  numbers  to  be  found 
are  comparatively  small.  In  certain  foreign  countries  very  effective 
work  is  reported  for  this  species,  and  colonies  recently  established  by 
Smith  in  California  give  promise  of  more  satisfactory  results  than 
followed  the  first  introduction. 

Scymnus  marginicollus  Mann. — This  native  species  is  often  found 
feeding  upon  the  younger  stages  of  the  various  mealy  bug  species, 
though  its  attacks  are,  in  general,  distributed  over  the  entire  group 
of  scale  insects.     Increase  in  numbers  under  normal  field  conditions 


^Childs,  Leroy,  Monthly  Bulletin  Cal.  Hort.  Com.,  Vol.  Ill,  No.  5,  p.  220, 
May,  1914. 

5  Smith,  H.  S.,  Monthly  Bulletin  Cal.  Hort.  Com.,  Vol.  Ill,  No.  12,  p.  535, 
December,  1914. 


MEALY   BUGS   OF    CITRUS    TREES  41 

is  not  rapid,  and  because  of  the  very  small  size  of  the  individuals  only 
a  comparatively  small  number  of  eggs  and  larvae  of  the  mealy  bug 
are  consumed  by  a  single  beetle. 

Scymnus  sordidus  Horn. — Of  the  members  of  the  genus  Scymnus 
this  species  is  the  greatest  in  importance  as  an  enemy  of  the  mealy 
bug.  In  distribution  it  is  restricted  to  a  considerable  extent  to  Ven- 
tura, Los  Angeles,  and  Orange  counties.  In  appearance  the  adults 
are  dark  brown  in  color,  while  the  larvae  are  covered  with  the  coating 
of  waxy  filaments  characteristic  of  a  large  number  of  mealy  bug 
feeders. 

Chrysoplatycerous  splendens  How. — This  hymenopterous  parasite, 
on  the  basis  of  imperfect  records  as  to  its  first  appearance  in  this 
country,  was  introduced  into  California  from  the  Philippine  Islands 
by  Compere.  At  that  time  it  was  placed  only  in  San  Diego  County, 
but  at  the  present  time  specimens  may  be  found  generally  distributed 
in  small  numbers  over  all  of  southern  California. 

Miscellaneous. — Observed  as  occasional  feeders  upon  the  mealy  bugs 
are  the  following  coccinellids :  Chilocorus  bivulnerus  Muls.,  Hippo- 
damia  convergens  Guer.,  Rhizobius  lopanthae  Blaisd.,  Rhizobhis  ven- 
tralis  Er.,  Scymnus  nebulosus  Lee,  and  Novius  cardinalis  Muls. 

Determined  as  occasional  predaceous  enemies  were:  Hemerobius 
pacificus  Banks,  Leucopus  bellula  Will.,  Baccha  lemur  0.  S.,  and  sev- 
eral other  syrphids. 

Several  internal  parasites,  as  yet  undetermined,  were  secured  from 
P.  longispinus  Targ.  at  Pasadena  and  Santa  Barbara.  A  small  para- 
site of  P.  citrophilus  at  Uplands  was  determined  by  Mr.  P.  H.  Tim- 
berlake  as  Pseudaphycus  angelicus  How. 


THE  CONTROL  OF  MEALY  BUGS  ON  CITRUS  TREES 

FUMIGATION 

Comparative  Resistance  of  Species. — The  study  of  fumigation  with 
reference  to  the  control  of  mealy  bugs  naturally  gave  rise  to  the  ques- 
tion of  the  relative  resistance  of  the  various  species  to  the  effects  of 
hydrocyanic  acid  gas.  To  determine  this  point,  a  series  of  laboratory 
experiments  were  conducted,  in  which  a  fumigatorium  with  a  capacity 
of  25  cubic  feet  was  used.  Upon  the  basis  of  one  ounce  of  sodium 
cyanide  per  100  cubic  feet,  as  a  100  per  cent  schedule,  the  amount  to 
use  in  the  box  would  be  one-quarter  of  this,  or  7.5  gm.  cyanide  with 
11.2  c.c.  sulfuric  acid  and  15  c.c.  water,  the  1,  1.5,  2  formula  being 


42 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION 


used.  The  dosages  as  given  in  the  following  table  represent  the  per- 
centage of  the  above  amount  used.  The  most  resistant  species  of  the 
four  was  found  to  be  P.  citrophilus,  the  larvae  of  which  were  all  killed 
by  a  70  per  cent  dosage,  as  compared  with  60  per  cent  for  P.  citri. 
The  eggs  and  adult  females  were  the  first  to  succumb  to  the  effects 
of  the  gas,  while  the  male  pupae  were  the  last  killed.  In  connection 
with  this  table  attention  is  called  particularly  to  the  fact  that  the 
conditions  under  which  the  experiment  was  carried  out  simulate  in 
no  way  those  found  in  actual  practice,  and,  therefore,  it  should  not 
be  considered  that  the  dosages  given  are  in  any  degree  correlated  with 
field  practices,  in  which  leakage,  size  of  trees,  etc.,  are  very  important 
factors  in  the  determination  of  the  necessary  amount  of  materials  for 
use.  The  table  is  given  only  to  indicate  the  relative  mortality  of  the 
stages  of  the  different  species  produced  by  a  given  amount  of  gas  in 
an  air-tight  receptacle. 


Comparative  Eesistance  of  Species  to  Fumigation 

Figures  in  each  case  represent  percentages 

Capacity  of  fumigatorium,  25  cu.  ft. 


Time  of  Temper- 
experi-     ature, 
ments,        °  F. 
hour 

40 
per  cent 
dosage 

Temper- 
ature, 
o  F 

50 
per  cent 
dosage 

Temper- 
ature, 

o    p 

60 
per  cent 
dosage 

Temper- 
ature, 
o  F> 

70 
per  cent 
dosage 

P.  citri 

Eggs  

.      1 

68 

65 

100 

66 

64 

Larvae  

.      1 

68 

92 

65 

81 

66 

100 

64 

Male  pupae  ... 

.      1 

68 

65 

66 

71 

64 

100 

Adult  females. 

.      1 

68 

80 

65 

100 

66 

64 

P.  baker  i 

Eggs  

.      1 

68 

65 

100 

66 

64 

Larvae   

.      1 

68 

74 

65 

92 

66 

100 

64 

Male  pupae  ... 

.      1 

68 

65 

61 

66 

100 

64 

Adult  females. 

.      1 

68 

86 

65 

100 

66 

79 

64 

100 

P.  citrophilus 

Eggs  

.      1 

68 

65 

100 

66 

64 

Larvae   

.      1 

68 

65 

65 

85 

66 

98 

64 

100 

Male  pupae  ... 

.      1 

68 

65 

17 

66 

82 

64 

100 

Adult  females. 

.      1 

68 

57 

65 

91 

66 

100 

64 

P.  longispinus 

Larvae  

.      1 

68 

89 

65 

100 

66 

64 

Male  pupae  ... 

.      1 

68 

65 

87 

66 

100 

64 

Adult  females. 

..      1 

68 

94 

65 

100 

66 

64 

MEALY   BUGS    OF    CITRUS    TREES  43 

General  Orchard  Experience. — A  marked  conflict  in  prevailing 
opinions  among  growers  and  investigators  as  to  the  effectiveness  of 
fumigation  against  the  mealy  bug  was  brought  out  at  the  Emergency 
Fruit  Growers'  Convention  held  in  Ontario,  January  30,  1914.  Some 
growers  reported  very  satisfactory  results  from  the  use  of  a  three- 
quarters  to  a  full  schedule,  continued  for  a  period  of  two  hours,  the 
tent  being  recharged  at  the  end  of  the  first  hour.  On  the  other  hand, 
a  number  reported  very  unsatisfactory  results  with  this  method  of 
treatment,  even  after  several  fumigations  each  season.  Other  growers 
even  went  to  the  extreme  of  doubling  the  dosage  at  each  application, 
with  the  result  that  the  trees  and  fruit  were  severely  injured,  though 
live  mealy  bugs  still  remained.  During  the  past  season  considerable 
mealy  bug  fumigation  has  come  under  the  observation  of  the  writer, 
and  in  only  one  instance  were  the  results  secured  thorough  enough 
to  compensate  for  the  expense  of  the  treatment.  It  will,  therefore, 
be  seen  that  upon  the  basis  of  present-day  methods  and  practices 
fumigation  is  not  to  be  recommended  as  a  satisfactory  means  of  control, 
even  when  repeatedly  applied. 

SPRAYING 

On  the  basis  of  the  results  secured  during  the  past  season  and 
previously,  it  is  evident  that  the  application  of  certain  sprays  was 
uniformly  more  satisfactory,  both  as  regards  cost  and  efficiency,  than 
fumigation  with  hydrocyanic  acid  gas. 

Nozzles. — Inasmuch  as  the  force  with  which  the  spray  strikes  the 
mealy  bug  is  one  of  the  most  important  factors  in  spraying  work,  it 
is  very  evident  that  the  mist  spray  nozzles  are  of  very  little  value. 
A  nozzle  giving  a  well  centered  drive  spray  should  be  used.  In  the 
application  of  water  alone,  as  later  discussed,  the  M.  A.  C.  nozzle  was 
found  to  be  very  satisfactory.  This  nozzle  was  developed  in  Massa- 
chusetts for  use  against  the  gipsy  moth.  Under  200  pounds  pressure, 
about  five  gallons  of  solution  per  minute  is  used,  and  any  form  of 
stream  desired  may  be  secured. 

Kerosene  Emulsion. — This  spray  is  very  commonly  used  in  control 
work  against  various  scale  insects.  The  formula  ordinarily  used  is  as 
follows : 

Kerosene  (42°  Baume)  20  gals. 

Solid  whale  oil  soap  5  lbs. 

or 

Liquid  whale  oil  soap  1  gal. 

Water 200  gals. 


44  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

This  emulsion  is  so  well  known  as  to  require  no  directions  for  its 
preparations.  It  is  quite  effective  against  many  scale  insects  when 
thoroughly  applied;  yet  in  the  case  of  the  mealy  bug  the  results  were 
not  entirely  satisfactory.  The  penetrating  action  of  the  spray  was 
not  great,  it  being  necessary  to  remove  the  waxy  covering  of  the  mealy 
bugs  by  the  force  of  application  before  an  extensive  killing  could  be 
secured.  This  lack  of  penetration  is  also  a  serious  handicap  in  cases 
where  large  egg  masses  are  present,  it  being  evident  that  the  killing- 
only  of  those  on  the  outer  surface  will  have  little  effect  in  checking 
the  infestation.  However,  if  these  masses  are  not  present,  and  the 
bugs  are  present  in  only  small  numbers  upon  the  fruit  and  foliage, 
satisfactory  results  may  be  looked  for  when  the  application  is  thor- 
oughly made.  Considerable  care  must  be  exercised  in  the  use  of  this 
spray  during  the  hot  summer  months,  as  a  burning  of  the  fruit  may 
take  place  at  a  temperature  above  approximately  89°  F.,  particularly 
if  the  humidity  is  low.  In  the  coast  sections,  however,  little  trouble 
is  experienced  in  this  regard. 

Distillate  Emulsion. — The  following  formula  gives  the  concentra- 
tion ordinarily  used  in  citrus  spraying: 

Distillate  (32°  Baume)  4  gals. 

Liquid  whale  oil  soap  %  gal. 

or 

Solid  soap 5  lbs. 

Water 200  gals. 

This  emulsion  is  prepared  in  the  same  manner  as  that  of  kerosene 
and  is  often  used  in  preference  to  that  because  of  the  lesser  cost. 
Distillate  spraying  is  much  less  likely  to  do  injury  to  the  fruit  and 
foliage  in  the  coast  sections  than  in  the  interior  sections. 

Kerosene-Lime  Mixture. — The  formula  is  as  follows: 

Kerosene  (42°  Baume)  20  gals. 

Unslaked  lime  40  lbs. 

Water  200  gals. 

In  preparing  the  mixture  the  lime  is  gradually  slaked  in  a  barrel 
or  other  convenient  receptacle  and  thoroughly  mixed  to  a  creamy 
consistency.  For  convenience  in  handling,  a  mixture  of  one  pound 
of  lime  per  gallon  of  water  should  be  used.  The  necessary  quantity 
of  this  material  should  then  be  strained  and  placed  in  the  tank,  the 
kerosene  and  sufficient  water  to  cover  the  agitators  added,  and  the 
engine  started.  Three  or  four  minutes  will  be  sufficient  to  bring  about 
a  thorough  emulsification.  In  case  the  mixture  is  permitted  to  stand 
for  some  time,  the  lime  and  kerosene  which  it  has  absorbed  will  sink 


MEALY   BUGS   OF    CITRUS    TREES  45 

to  the  bottom  of  the  tank  and  a  thin  layer  of  frothy  lime  will  appear 
on  the  surface.  The  emulsion,  however,  is  stable  and  requires  only 
agitation  to  be  ready  for  use. 

The  use  of  lime  as  the  emulsifying  agent  instead  of  soap  was 
found  to  increase  considerably  the  penetration  of  the  waxy  covering 
of  the  mealy  bugs.  Where  large  egg  masses  are  found  upon  the  fruit 
and  twigs,  the  penetration  will  not  be  complete  by  the  first  application, 
but  a  thin  crust  of  lime  will  be  formed  over  the  surface,  which  will 
prevent  the  exit  of  the  young  mealy  bugs  from  the  navels  of  the 
oranges.  The  white  coating  of  lime  deposited  over  the  entire  tree 
brought  out  strongly  the  fact  that  in  field  spraying  as  ordinarily 
practiced  the  uppermost  branches  in  the  center  of  the  tree  were  very 
often  left  unsprayed,  and  as  a  result  the  possibilities  of  a  rapid  re- 
infestation  were  very  good.  The  presence  of  some  indicator  in  the 
spray  is  particularly  desirable  in  mealy  bug  control  work,  where 
application  to  every  portion  of  the  tree  is  a  prime  necessity. 

It  is  evident  that  a  thorough  washing  or  brushing  of  the  fruit  will 
be  necessary  following  the  application  of  this  spray,  and  its  use  is, 
therefore,  inadvisable  where  the  infestation  is  not  severe  enough  to 
require  the  washing  when  unsprayed.  This  emulsion  has  been  found 
to  be  the  most  satisfactory  and  efficient  of  all  "composition"  sprays 
tested,  and  is  to  be  recommended  in  cases  of  heavy  infestation,  in 
which  for  any  reason  the  use  of  large  quantities  of  water  alone,  as 
later  discussed,  is  not  possible. 

Carbolic  Acid  Emulsion. — Varying  results  have  been  reported  for 
this  material  as  a  mealy  bug  spray  for  many  years,  some  claiming  it 
to  be  very  efficient  and  others  insisting  strongly  that  it  is  of  very  little 
value.     The  formula  ordinarily  used  is  as  follows: 

Crude  carbolic  acid  5  gals. 

Liquid  whale  oil  soap  8  gals. 

or 

Solid  whale  oil  soap  40  lbs. 

Water 40  gals. 

The  soap  should  be  added  to  the  boiling  water  and  the  crude  car- 
bolic acid  then  poured  in  and  allowed  to  boil  for  ten  to  twenty  minutes. 
This  stock  solution  should  then  be  diluted  with  twenty  parts  of  water 
for  spraying  purposes. 

The  number  of  infested  trees  treated  by  the  writer  with  this 
emulsion  was  142,  and  the  results  secured  were  decidedly  negative ; 
in  fact,  of  all  spray  materials  used  this  emulsion  effected  the  least 
killing.    Even  though  the  wax  was  completely  removed  from  the  mealy 


46  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

bugs  by  the  force  of  the  spray,  many  survived  to  continue  the  infes- 
tation. 

A  series  of  samples  of  crude  carbolic  acid  were  sent  to  Mr.  G.  P. 
Gray,  chemist  of  the  insecticide  laboratory,  for  analysis.  The  specific 
gravity  of  these  samples  at  17.5°  C.  ranged  from  .920  to  .965,  while 
the  total  phenol  content  varied  correspondingly  from  1.2  per  cent  to 
18.6  per  cent.  The  ratio  of  increase,  however,  was  not  constant.  The 
following  comments  by  Mr.  Gray  are  of  interest:  "The  variation  in 
these  samples  is  no  greater  than  might  be  expected  in  the  purchase 
of  crude  carbolic  acid  as  found  on  the  market.  Previous  examination 
by  this  laboratory  of  a  great  many  samples  shows  an  even  greater 
variation  than  the  above,  the  range  being  from  4.5  to  38  per  cent.  .  .  . 
No  uniformity  of  results  can  be  expected  from  the  crude  carbolic  acids 
and  the  coal  tar  creosotes  as  commonly  produced  in  the  United  States. 
Most  of  the  materials  sold  under  the  two  above  names  appear  to  be 
mixed  residues  from  coal  tar  refineries,  which  cannot  be  sold  for  any 
other  purpose,  and  also  are  quite  frequently  mixed  with  petroleum 
distillates.  I  am  not  sure  that  the  phenol  is  the  most  active  agent  iD 
the  control  of  the  mealy  bug." 

In  connection  with  the  use  of  carbolic  acid  in  the  proportion  given 
above,  considerable  burning  of  fruit  occasionally  takes  place,  and  in 
some  cases  the  acid  odor  and  taste  may  be  detected  several  months 
after  its  application. 

Water. — The  most  efficient  means  of  control  for  mealy  bugs  known 
at  the  present  time  is  the  application  of  large  quantities  of  water 
under  high  pressure.  In  the  investigations  conducted  by  the  writer, 
a  total  of  347  trees  were  sprayed  with  water  under  varying  degrees 
of  pressure  and  methods  of  application. 

Under  the  direction  of  Horticultural  Inspector  A.  G.  Smith  of 
Pasadena,  several  groves  at  that  place  were  equipped  with  a  complete 
piping  system,  this  consisting  of  a  one-inch  underground  pipe  line 
along  the  head  of  the  grove  and  three-quarter  inch  laterals  leading 
down  every  fourth  row.  An  ordinary  garden  hydrant  was  placed  at 
every  fourth  tree,  thus  enabling  the  operator  to  reach  every  tree  in 
the  grove  with  a  hose  line  125  feet  in  length.  In  these  particular  cases 
the  necessary  power  was  secured  from  an  ordinary  power  spray  outfit 
near  the  irrigation  hydrant,  a  float  valve  being  used  in  connection  with 
the  intake  hose  to  regulate  the  amount  in  the  tank,  and  the  water  then 
pumped  directly  into  the  main  pipe  line  under  high  pressure.  The 
main  argument  against  this  system  is  the  rather  large  initial  cost  of 
the  equipment,  which  may  possibly  be  needed  for  only  one  or  two 
years,  the  degree  of  infestation  varying  greatly  from  year  to  year. 


MEALY   BUGS   OF    CITRUS    TREES  47 

This  has  been  well  illustrated  in  Ventura  County,  where  five  years 
ago  the  attack  of  the  pest  was  very  severe,  yet  a  general  decline  has 
taken  place  since  then,  and  at  the  present  time  not  so  many  groves 
are  seriously  enough  infested  to  require  control  measures.  It  is,  there- 
fore, not  recommended  that  this  equipment  be  installed  unless  it  may 
also  be  used  for  irrigation  purposes,  as  is  the  case  in  certain  localities, 
or  where  experience  over  a  considerable  period  of  years  has  shown 
that  the  pest  will  maintain  itself  in  damaging  numbers  from  year  to 
year. 

A  modified  form  of  this  system  and  one  which  will  materially 
reduce  the  cost  of  installation  is  the  use  of  the  long,  sectional  hose 
lines  in  place  of  the  underground  lateral  pipe  lines.  Galvanized  one- 
inch  pipe  may  be  used  for  the  main  line,  the  additional  initial  cost 
being  well  compensated  for  by  the  increased  durability.  Half-inch 
hose  of  the  best  quality  should  be  used  in  sections  of  about  100  feet, 
with  an  occasional  shutoff  to  facilitate  the  work.  In  the  work  in  the 
field,  the  line  should  be  run  its  full  length  down  the  rows  and  the 
trees  at  the  lower  end  sprayed  first.  As  a  matter  of  convenience,  uot 
more  than  two  rows  on  each  side  should  be  taken,  and  when  a  sufficient 
number  have  been  sprayed  a  section  of  hose  may  be  removed  and  the 
work  thus  continued  up  the  rows.  In  case  a  regulation  power  sprayer 
is  available,  this  may  be  used  according  to  directions,  as  previously 
given.  If  the  purchase  of  an  outfit  is  necessary,  however,  it  would 
be  well  to  secure  a  standard  pumping  outfit  of  the  required  power 
rather  than  to  go  to  the  expense  of  securing  the  complete  outfit.  The 
methods  of  attachment  and  the  position  with  reference  to  the  water 
supply  vary  so  greatly  that  no  general  directions  can  be  given,  and 
arrangements  must  be  made  to  suit  conditions  existing  in  every  grove. 

The  cost  of  installing  the  pipe  system  ranges  from  $15  to  $25  per 
acre,  while  the  cost  of  spraying  after  this  time  will  total  approxi- 
mately $2.25  per  day  for  every  man's  labor,  and  also  the  cost  of  run- 
ning the  engine.  Allowing  for  twenty  minutes'  time  in  the  spraying 
of  every  tree,  this  would  cost  about  15  cents  per  tree,  which  cannot 
be  considered  excessive. 

Where  the  infestation  is  restricted  to  small  areas,  the  use  of  the 
regulation  spray  outfit  is  the  most  economical  and  satisfactory.  In 
connection  with  this,  there  should  be  a  supply  wagon  for  hauling  water 
to  the  tank,  as  the  time  required  in  transit  and  in  filling,  where  this 
is  done  with  the  tank  itself,  is  wasteful,  necessitating  as  it  does  the 
cessation  of  work  by  the  engine  and  the  men  handling  the  hose  lines. 
The  large  amount  of  material  used  makes  this  equipment  very  de- 
sirable. 


48  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

In  the  application  of  water  as  a  means  of  control  too  much  em- 
phasis cannot  be  laid  upon  the  necessity  of  thorough  application.  The 
pressure  with  the  M.  A.  C.  nozzles  should  never  be  less  than  175  pounds, 
while  considerably  higher  pressure  would  be  advantageous.  The  form 
of  stream  used  should  be  such  as  to  give  a  spread  of  not  more  than 
six  or  eight  inches  at  a  distance  of  six  feet  from  the  nozzle.  The 
amount  of  water  applied  will  naturally  vary  considerably  with  the 
size  of  the  tree  and  the  severity  of  the  infestation.  In  the  case  of  a 
medium-sized  tree,  50  to  100  gallons  is  necessary  to  wash  the  tree 
thoroughly. 

The  treatment  should  be  repeated  as  soon  as  the  egg  masses  and 
adults  begin  to  appear  in  any  considerable  numbers  on  the  tree.  The 
number  of  applications  necessary  will  naturally  vary  with  the  degree 
of  the  infestation. 

SUMMARY 

1.  Four  species  of  mealy  bugs  feed  upon  citrus  trees  in  Southern 
California — P.  citri,  P.  bakeri,  P.  citrophilus,  and  P.  longispinus. 

2.  By  far  the  greatest  amount  of  injury  is  caused  by  the  common 
mealy  bug  (Pseudococcus  citri). 

3.  The  infestation  at  Uplands,  California,  was  found  to  be  caused 
by  a  new  species,  now  designated  as  the  citrophilus  mealy  bug  (Pseu- 
docuccus  citrophilus). 

4.  The  life  history  during  the  summer  covers  approximately  two 
months,  the  egg  stage  requiring  8  to  10  days  and  the  nymphal  stages 
a  total  of  about  50  days. 

5.  Maximum  numbers  are  ordinarily  found  upon  the  trees  during 
the  early  spring  and  late  fall  months. 

6.  The  spread  from  one  grove  to  another  is  effected  upon  picking 
boxes,  pickers'  clothing,  cultivating  tools,  by  birds,  etc. 

7.  Parasites  at  the  present  time  are  not  very  effective  in  mealy- 
bug control,  and  their  work  should  not  be  relied  upon  to  the  exclusion 
of  artificial  control  methods  where  the  infestation  is  serious. 

8.  Fumigation  with  hydrocyanic  acid  gas  is  not  to  be  recommended. 

9.  The  citrophilus  mealy  bug  is  more  resistant  to  hydrocyanic  acid 
gas  than  any  of  the  three  other  species. 

10.  Spraying  with  water  under  high  pressure,  using  the  M.  A.  C. 
nozzle,  is  the  most  effective  means  of  control,  and  when  thoroughly 
done  gives  a  considerable  degree  of  success. 

11.  Treatment  should  be  repeated  whenever  the  injury  produced 
by  the  insect  becomes  sufficient  to  warrant  the  expense. 


